Conventionally, active energy ray-curable inkjet ink has been installed on high-speed printing type signage printers from the viewpoint of the speed of dryness and the reduction of environmental load as compared with the solvent type ink. Alternatively, the active energy ray-curable inkjet ink is installed on a flat bed type printer corresponding to various base materials from the viewpoint that base material adhesion property is excellent. Then, development of ink formula according to these applications has been made.
However, printed matter having poor in leveling property of dots, glossing property, and color reproductivity has been obtained very often because of the speed of dryness. Therefore, quality of printing has not been acceptable in the market in some cases. In particular, it has been difficult to be applied to the market of high-quality printing.
In order to solve this problem, in printers in which a head scans a base material and superimposition printing is carried out, it has been possible to obtain high quality images by adjusting deposition positions of dots, lamp timing, or the like. However, since in one-pass type printers, which have been developed in recent years, dots of each color are printed in one layer, it has been difficult to adjust deposition positions of dots and hardening timing, so that it has not been possible to obtain high quality images.
Furthermore, when printing is carried out on coated paper and cast paper having a coated layer, due to unevenness in painting or variation in the surface state of the coated layer, ink spreads in indefinite directions, so that dots which cannot be controlled are formed. As a result, it was not possible to obtain printed matter having high image quality.
Hereinafter, approaches for obtaining high image quality in ink-jet printing disclosed before the present invention was made are described.
Patent Literature 1 discloses an approach for obtaining printed matter having high image quality by controlling the surface tension of each color in water-based ink, thereby controlling spread or penetration of colors. However, since this invention controls the penetration, leveling of dots at the time of drying cannot be sufficiently controlled, so that small dots are formed. With this method, in superimposing printing, ink for complementing between dots can be subjected to printing repeatedly. However, when printing is carried out by using a one-pass type printer, superimposing printing of the same color cannot be carried out. Therefore, in ink whose leveling of dots is controlled, stripes remarkably occur in 100% printed portion. Furthermore, because leveling of dots are suppressed, a beading phenomenon in which dots originally occurring in 10 to 30% printed portion are fused to each other occurs in 50 to 80% printed portion. As a result, printed matter with an extremely low quality of image was obtained. Furthermore, since the amount of a surface-active agent to be used was small, when printing is carried out on coated paper, remarkable distortion of dots occurred. When the surface-active agent was added to an active energy ray-curable ink of the present invention, the function of adjusting the surface tension was not able to be sufficiently obtained, thus making controlling impossible.